The aim of this work is to investigate the molecular mechanisms which underlie the function of K+-selective ion channels. minK is uniquely suited for this purpose. As its name suggests, the minimalK channel is the smallest and simplest eukaryotic K+ channel known. Thought to be a delayed rectifier underlying cardiac repolarization, it is a highly selective, voltage-gated K+ channel; yet, this remarkable protein has only 130 amino acids and only a single potential transmembrane domain. This work will exploit the small size of minK to facilitate the identification and study of protein domains which accomplish the two essential tasks of ion channels: conduction and gating. The tools of this work are site-directed mutagenesis (using a synthetic gene for minK to facilitate recombinant DNA work) with expression in Xenopus oocytes and electrophysiologic assessment. We will strive to identify residues which contribute to the pore, voltage- sensor and gating structures of minK. We will start at amino acid positions we have previously shown to affect the function of each of these structures. The most interesting mutants will be studied in mechanistic detail in isolated oocyte membranes with recently developed techniques. Ultimately, we hope to purify and reconstitute the channel into model membranes to study its single-channel behavior and characterize it at the protein-biochemical level.